Modelling Co-Infection of the Cystic Fibrosis Lung by Pseudomonas aeruginosa and Burkholderia cenocepacia Reveals Influences on Biofilm Formation and Host Response

Abstract

The Gram-negative bacteria Pseudomonas aeruginosa and Burkholderia cenocepacia are opportunistic human pathogens that are responsible for severe nosocomial infections in immunocompromised patients and those suffering from cystic fibrosis (CF). These two bacteria have been shown to form biofilms in the airways of CF patients that make such infections more difficult to treat. Only recently have scientists begun to appreciate the complicated interplay between microorganisms during polymicrobial infection of the CF airway and the implications they may have for disease prognosis and response to therapy.To gain insight into the possible role that interaction between strains of P. aeruginosa and B. cenocepacia may play during infection, we characterised co-inoculations of in vivo and in vitro infection models. Co-inoculations were examined in an in vitro biofilm model and in a murine model of chronic infection. Assessment of biofilm formation showed that B. cenocepacia positively influenced P. aeruginosa biofilm development by increasing biomass. Interestingly, co-infection experiments in the mouse model revealed that P. aeruginosa did not change its ability to establish chronic infection in the presence of B. cenocepacia but co-infection did appear to increase host inflammatory response.Taken together, these results indicate that the co-infection of P. aeruginosa and B. cenocepacia leads to increased biofilm formation and increased host inflammatory response in the mouse model of chronic infection. These observations suggest that alteration of bacterial behavior due to interspecies interactions may be important for disease progression and persistent infection.

Thymidine-Dependent Staphylococcus aureus Small-Colony Variants Are Induced by Trimethoprim-Sulfamethoxazole (SXT) and Have Increased Fitness during SXT Challenge

“…The agar bead chronic pneumonia mouse model was used for competition experiments between the WT (S. aureus SH1000) and the ⌬thyA mutant (27). A starting amount of 5 ϫ 10 9 ⌬thyA mutant cells/WT bacteria, mixed at a 1:1 ratio, was used for inclusion in the agar beads prepared according to a method described previously for P. aeruginosa, with modifications (28,29). Briefly, S. aureus strains were cultured in BHI broth with erythromycin (2.5 /ml) for the mutant and without erythromycin for the WT overnight at 37°C, adjusted to a starting OD 600 of 0.1, grown for an additional 3 h (SH1000) and 5 h (⌬thyA mutant) to allow agar bead preparation.…”

The Limitations of In Vitro Experimentation in Understanding Biofilms and Chronic Infection

“…In other models, differences are also observed. For instance, co-colonisation of two common CF pathogens (P. aeruginosa and Burkholderia cenocepacia) in a murine CF model leads to a mutualistic relationship, whereby P. aeruginosa persists, and B. cenocepacia alters the inflammatory response [102]. In some instances, the presence of multiple species within a specified environment is a necessity.…”

Biofilm models of polymicrobial infection

“…In one study, P. aeruginosa and Burkholderia cenocepacia, two species frequently found together in severe CF infections, were suspended together in agar-bead solutions, and then inoculated into the trachea of mice [111]. The coinfection showed increased biofilm formation and inflammation, possibly due to interactions between the two opportunistic species.…”